I really don't think anything in a lucid dream could convince me of the existence of God; I would be inclined to think, as a sceptic, that the most likely explanation for any given numinous experience via lucid dreaming would be a product of my own mind.

"Empty cognizance of one taste, suffused with knowing, is your unmistaken nature, the uncontrived original state. when not altering what is, allow it to be as it is, and the awakened state is right now spontaneously present."

I think this has happened before, actually (or, I should say, apparently). In the Bible, many people had visions where God told them to do something and they did it and it played out like God said it would. I'm just mentioning the Bible because I think the type of thing you are describing would play out like such an event described in the Bible; namely, that in the lucid dream God would tell you something and in real life that thing actually happens. Of course, such an event would only prove God's existence to you as the person who actually experienced the lucid dream (and even then it might take it happening a couple of times before you ruled out the possibility of coincidence, depending on your level of skepticism).

Also, the extent of proof to self should be given proper weight. Power for precognition, of itself, does not necessitate even a good source. Experience is nice, but should be secondary to more objective witness, such as redemptive history. I refer to the messianic milieu out of ancient writings, and potential association to Jesus.

John the Baptist, from prison, sent people to Jesus to ask: "Are you the one ...to come, or should we expect someone else?" (Luke 7:18). Rather than blast John as a doubting unbeliever, Jesus said that no greater human ever existed (Luke 7:28). Honest doubt and inquiry can lead to stronger beliefs.

"Empty cognizance of one taste, suffused with knowing, is your unmistaken nature, the uncontrived original state. when not altering what is, allow it to be as it is, and the awakened state is right now spontaneously present."